This invention relates to a process and a catalyst composition used in the process for the hydroprocessing of a heavy hydrocarbon feedstock. Another aspect of the invention includes a catalyst support material that can be used as a component of the hydroprocessing catalyst composition to impart certain physical properties, which make the hydroprocessing catalyst composition particularly useful in the hydroprocessing of a heavy hydrocarbon feedstock.
The catalytic hydrotreatment of hydrocarbon feedstock in order to remove therefrom impurities such as sulfur, nitrogen, and metal compounds is a commonly used process to improve or upgrade such hydrocarbon feedstock. In a typical hydrotreating process, the hydrocarbon feedstock is contacted in the presence of hydrogen with a hydrotreating catalyst under process conditions that suitably provide for a treated hydrocarbon product. The hydrotreating catalysts used in these processes generally are composed of an active phase that can include a component from the Group VIB metals and a component from the Group VIII metals supported on a porous, refractory inorganic oxide material.
The hydrotreatment of heavy hydrocarbon feedstock is particularly difficult; because, such feeds tend to have high concentrations of contaminating sulfur and metal compounds and may require the use of more severe process conditions than those needed to treat lighter hydrocarbon feedstock. Also, the heavy hydrocarbon feedstock can contain a heavy boiling fraction which a portion thereof is to be converted into lighter and more valuable components. As a result of the particular characteristics of a heavy hydrocarbon feedstock, the hydroprocessing of such a feedstock using a hydroprocessing catalyst will tend to cause its catalytic activity to decline at a rapid rate. This rate of decline in catalytic activity can be an indicator of catalyst stability. A catalyst exhibiting a low rate of decline in catalytic activity is thought of as having a high stability, and a catalyst exhibiting a high rate of decline in catalytic activity is thought of as having a low stability. It is desirable for a catalyst to be highly stable.
The use of ebullating bed reactor systems in the hydrotreatment of a heavy hydrocarbon feedstock has been proposed. In these systems, the heavy hydrocarbon feed is introduced in an upflow direction at the bottom of a catalyst bed contained within a reaction zone in a manner so as to lift or expand the catalyst bed to thereby form a fluidized bed of the catalyst. The heavy hydrocarbon passes through the expanded bed of catalyst into a separation zone wherein the product is separated from the catalyst and liquid hydrocarbon. The liquid hydrocarbon passes through a downcomer to a recycle ebullation pump and is recycled and reused in the expansion of the catalyst bed. It is important in the proper operation of the ebullating bed reactor system for the catalyst particles to have a bulk density within a certain range. The bulk density must be high enough to avoid substantial carryover of catalyst particles with the separated product but not so high as to require unreasonably high feed space velocities to provide for bed expansion.
It is also desirable for the hydrotreatment process to provide for the conversion of at least a portion of the heavy hydrocarbon compounds of a heavy hydrocarbon feed to lighter hydrocarbon compounds. There are those who have presented various hydrotreatment and hydroconversion catalyst compositions for use in the hydroprocessing of heavy hydrocarbon oils. For instance, WO 00/44856 (Nippon Ketjen and Akzo Nobel) discloses a hydroprocessing catalyst that comprises 7 to 20% of a Group VIB metal component (Mo, W, Cr), 0.5 to 6% Group VIII metal component (Ni, Co, Fe), and 0.1 to 2% alkali metal component supported on a carrier of at least 3.5% silica and which has a surface area of at least 150 m2/g, a total pore volume of at least 0.55 ml/g, and a pore size distribution such that 30-80% of the pore volume is present in the pores having a diameter of 100-200 Angstroms and at least 5% of the pore volume is present in the pores having a diameter of above 1000 Angstroms. An important feature of this hydroprocessing catalyst is its silica and sodium content.
U.S. Pat. No. 4,549,957 (Amoco Corporation) discloses a process and catalyst for the hydrotreating of feeds containing high concentrations of metals and sulfur. The hydrotreating catalyst comprises a hydrogenation component on a support having specific required physical properties including a BET surface area of 150 to 190 m2/g, a pore volume of 0.9 to 1.3 cc/g in the micropores having radii up to 600 Angstroms, with at least 0.7 cc/g of such micropore volume in micropores with radii ranging from 50 to 600 Angstroms, a macropore volume of 0.15 to 0.5 cc/g in macropores having radii of 600 to 25,000 Angstroms, and a total pore volume of 1.05 to 1.8 cc/g. The micropore distribution of this catalyst is indicated to be important to its demetalization activity, but the precise composition of the support is indicated as being relatively unimportant.
U.S. Pat. No. 4,066,574 (Chevron Research Company) discloses a hydrodesulfurization process that uses a catalyst containing a Group VIB metal and a Group VIII metal on a support material that has at least 70 vol. % of its pore volume in pores having a diameter between 80 and 150 Angstroms and less than 3 vol % of its pore volume in pores having a diameter above 1000 Angstroms. There is no mention of the surface area of the catalyst and the patent states that the support material may include silica suggesting that there is no critical concentration thereof in the support material.
There is a continuing need to develop hydrotreating catalyst compositions that have improved properties over prior art catalysts such as better catalytic activity and stability. There is also an ongoing need to develop improved catalyst compositions and processes that provide for the hydrotreating and hydroconversion of heavy hydrocarbon feedstock.